This invention relates generally to combined-cycle power generation systems, and more specifically, to systems and methods for channeling steam into turbines.
At least some known combined-cycle power systems include at least two gas turbine engines and at least one steam turbine engine. Each gas turbine engine is coupled in flow communication with a heat recovery steam generator (“HRSG”), which facilitates generating steam. Specifically, exhaust gases from each gas turbine engine are channeled into the corresponding HRSG to generate steam for use in other power plant processes such as, but not limited to, driving a steam turbine.
In at least some known combined-cycle power systems, a first gas turbine engine is designated as a lead gas turbine engine and a second gas turbine is designated as a lag gas turbine. Steam generated by the exhaust gases discharged by the lead gas turbine initially powers the steam turbine, and steam generated by the exhaust gases discharged by the lag gas turbine is channeled into the steam turbine at a later time. In at least some known combined-cycle systems, blending the lag gas turbine steam into the steam turbine produces temperature gradients within various steam turbine components. Depending on the temperature range of the gradients, thermal stresses may be induced within the steam turbine. Furthermore, a flow rate of the blended steam may also produce stress within the steam turbine. Moreover, depending on the temperature of the steam, over time, such stresses may reduce the useful life of steam turbine components and/or may adversely effect the efficiency of the turbine.
To prevent thermally stressing the steam turbine, at least some known combined-cycle power systems manually blend the steam generated within the lag HRSG over an extended period of time. However, slowly blending the lag steam into the steam turbine may result in reducing the overall efficiency of the power system.